Graphics Processing Unit (GPU)
Drawing processor and display controller of the PlayStation.
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Overview
The PlayStation has two graphics processors: the GPU and the GTE (Geometry Transformation Engine).1
The GPU draws polygons and sprites into the frame buffer. It also displays areas of the frame buffer on the screen.1
The GTE is a coprocessor of the CPU. It calculates coordinate data and light source data.1
Frame Buffer
The GPU has 1 MB of video memory (VRAM).1
The frame buffer is 1024 x 512 pixels.2
The frame buffer is dual ported. The GPU can draw into it while the display reads from it.1
DMA can transfer data between the frame buffer and main memory.1
Display Area
The GPU displays a rectangular area of the frame buffer on the screen. Sony calls this area the display area.1
Screen Modes
The GPU supports the following screen modes:
| Mode | Standard resolution (NTSC) | Remarks |
|---|---|---|
| 0 | 256 x 240 | Non-interlace |
| 1 | 320 x 240 | Non-interlace |
| 2 | 512 x 240 | Non-interlace |
| 3 | 640 x 240 | Non-interlace |
| 4 | 256 x 480 | Interlace |
| 5 | 320 x 480 | Interlace |
| 6 | 512 x 480 | Interlace |
| 7 | 640 x 480 | Interlace |
| 8 | 384 x 240 | Non-interlace |
| 9 | 384 x 480 | Interlace |
Display Colors
The GPU has two display color modes: 15-bit direct and 24-bit direct.3
15-bit Direct Mode
15-bit direct mode displays up to 32,768 colors.3
The GPU computes color in 24 bits and dithers the result. The display comes close to 24-bit color.3
24-bit Direct Mode
24-bit direct mode displays up to 16,777,216 colors.3
The GPU cannot draw in this mode. Drawing assumes 16 bits per pixel.3
This mode displays image data that was transferred into the frame buffer.3
Frame buffer coordinates stay in 16-bit units. A 640 x 480 image in 24-bit mode occupies 960 x 480 in the frame buffer.3
Drawing Functions
The GPU has the following drawing functions:
| Name | Description |
|---|---|
| Sprite drawing | 1 x 1 to 256 x 256 pixels. 4-bit CLUT (16 colors per sprite), 8-bit CLUT (256 colors per sprite) or 15-bit direct (32,768 colors per sprite). |
| Polygon drawing | Flat shading. Gouraud shading. Texture mapping. |
| Line drawing | Gradation. |
| Image transfer | CPU to frame buffer. Frame buffer to CPU. Frame buffer to frame buffer. |
| Other | Blending (translucency). Dithering. Clipping. Offset specification. |
Drawing Coordinates
Drawing coordinates are signed 11-bit values. X and Y range from -1024 to 1023.2
The coordinate offset sets the drawing origin anywhere in the frame buffer.2
The GPU clips all drawing to the current drawing area.2